Immunoglobulins from the sera and body secretions of an evolutionary intermediate species, chickens, will be examined as to immunoglobulin C-region complexity, evolution, and biological functions in relation to immunoglobulins of mammals, particularly humans. Immunological and chemical techniques will be utilized to examine the intact molecules as well as heavy chains, light chains, and enzymatic fragments. Chicken immunoglobulins will continue to be examined for the presence of separate gene duplications (products giving rise to immunoglobulin classes and subclasses). Fc regions of chicken IgC will continue to be examined for sequence homologies with mammalian gamma chains. Studies are designed to determine IgA levels, structural nature, and distribution in embryonic, normal adult, and immune deficient chickens. The immunoglobulin profile of immune deficient chickens will be examined with emphasis on the presence of a 5S immunoglobulin-like protein and on determining whether the gene controlling the J chain is repressed in conjunction with the absence of gamma chains. Surgically and chemically bursectomized chickens will be examined for the presence of lymphoid cells expressing the Fc receptor which is B cell specific in normal chickens. Sera from several avian and reptilian species will be examined to determine immunoglobulin reactivity with chicken Fc recptors. BIBLIOGRAPHIC REFERENCES: Sanders, B. G. and J. C. Travis, 1975. Evidence for one immunoglobulin light chain type in chickens: Absence of a blocked N-terminal light chain type. Biochem. Gen. 13: 779-782. Travis, J. C. and B. G. Sanders, 1975. Sequence of the cysteine peptides from the chicken 7.8S Ig heavy chain C-region: A comparison with the gamma chain of humans. Int. J. Biochem. 6: 719-722.